Managing performance and reliability in enterprise-grade Java applications often depends on how well we handle sessions, caching, and routing. In IBM WebSphere environments, three key components play distinct but interconnected roles: Stored Sessions, Dynamic Cache, and the IBM HTTP Server (IHS).

Let’s break down what each does, how they differ, and how they work together in clustered or high-availability deployments.

 1. WebSphere Stored Session

Purpose:
Stored Sessions manage user-specific state during a browsing session — such as authentication, user preferences, or workflow progress.

Storage Options:

• In-Memory (default): Stored in the JVM heap. Fast but not shared between nodes.
• Database Persistence: Sessions saved to a shared database, ensuring continuity after failover.
• Memory-to-Memory Replication: Real-time replication of session data across cluster members.
• External Session Store: For cloud-native environments (e.g., Redis, eXtreme Scale).

When It Matters:
If one application server goes down, persistent or replicated session storage ensures users don’t lose their active sessions.

 2. WebSphere Dynamic Cache (DynaCache)

Purpose:
Dynamic Cache (or DynaCache) improves performance by caching servlet fragments, JSPs, or frequently accessed data so that WebSphere doesn’t reprocess the same logic for every request.

Key Features:

• Can cache at multiple levels (page, fragment, or data).
• Uses Data Replication Service (DRS) to synchronize cached data between cluster nodes.
• Integrates with WebSphere eXtreme Scale for large distributed cache grids.

When It Matters:
Caching drastically reduces backend calls, making applications faster and more scalable — especially under heavy load.

 3. IBM HTTP Server (IHS)

Purpose:
IHS acts as the front-end web gateway for WebSphere Application Server.

Core Functions:

• Handles HTTP/HTTPS requests and SSL/TLS termination.
• Routes application traffic to backend WebSphere cluster nodes using the WebSphere Plugin.
• Implements session affinity (sticky sessions) using the JSESSIONID cookie.
• Serves static content (HTML, JS, images) directly.
• Provides simple static caching, but not session or application-level caching.

When It Matters:
IHS helps balance load, offload SSL processing, and improve performance by routing requests efficiently across nodes.

 How They Work Together

Architecture Diagram

Flow:

1. A user request hits IHS → routed to one WebSphere node via plugin-cfg.xml.
2. Sticky session ensures repeat requests go to the same node.
3. WebSphere retrieves session data (stored/replicated).
4. Dynamic Cache accelerates data retrieval from prior computations.
5. If session or cache is unavailable, the backup database or cache grid serves it.

Summary

Together, these three layers make IBM WebSphere a robust, scalable, and resilient middleware platform — balancing user session continuity, performance, and availability